A separated coil between the transmitting side and the receiving side (transmitting and receiving separated coil, hereinafter referred to as a separated coil) is often used as an inspection coil of NMR signal.
Such transmitting and receiving separated coils have been electrically and magnetically combined or coupled. The matching with a resonance circuit connecting between the transmitting side coils and the receiving side coils may be difficult. There may be leaks of magnetic field from the transmitting side coils to the receiving side coils at the time of irradiation of magnetic field intensity as being a transmitting signal. In such a case, a preamplifier connected to the receiving coils may be saturated by the irradiated magnetic field intensity. Then, the preamplifier may result in a condition impossible for being temporarily or permanently used.
It is necessary to degrade the above combination or coupling in the transmitting and receiving separated coils in order to solve the above problems.
Various technical arts described in U.S. Pat. No. 7,388,377 B2 has been known as a technical art to degrade the combination or coupling of the above transmitting and receiving separated coils. In the above Publication, the spectroscopic transmitting and receiving coils of NMR (hereinafter referred to as a NMR probe) for switching between the transmitting and receiving conditions of RF with use of a diode switch as a switch part has been disclosed. This technical art is designed to arrange a diode switch in a tuning and matching circuit resonating RF antenna coil at a specific frequency, and is a circuit for changing a resonance condition.
The NMR probe is required to be arranged in the strong magnetic field intensity. However, when magnetic field intensity goes beyond the prescribed intensity or the temperature goes beyond the prescribed temperature range, the phenomena to degrade the quality of a diode switch as a switch part have been already known. In the technical art described in the above publication, a diode switch for switching between the transmitting and receiving conditions of RF transmitting and receiving circuit is arranged inside or near the tuning and matching circuit in the strong magnetic field. For this reason, the tuning and matching circuit becomes large, when the diode switch is arranged to be far away in the magnetic field to be accurately operated. That is, it is problems to become too long in a circuit length of the tuning and matching circuit and deteriorate the quality factor (Q value) of the tuning and matching circuit.
Considering the above, an object of the present invention is to easily switch ON or OFF of the tuning and matching at the time of use or nonuse.